At present, water-based paint compositions are replacing solvent-based paint compositions, as a paint, particularly in paint used for spraying automobiles. It is considered that this trend will increase in view of heightened awareness of the painting environment, the work environment and environmental pollution.
In general, polymer particles are often formulated in water-based (aqueous) paint compositions so as to improve paint workability. However, such a formulation of polymer particles always involve problems such as agglomeration, separation, thickening and the like. U.S. Pat. No. 4,403,003 discloses fine particles having a particle size of 0.01 to 10 .mu.m which are formulated in a metallic-based paint. These fine particles ate produced according to a double-stage emulsion polymerization wherein core resin particles are formed and then a water-soluble polymer layer is formed thereon, to improve dispersion stability in an aqueous medium. However, the double-stage polymerization method is not practical because of its complicated operation. Further, the stability and the paint viscous property in an aqueous paint of particles, thus obtained, may not necessarily be sufficient.